Having the viewers switch by default is useful for demos, when you are showing something to someone. And it's the simplest behaviour for their data structure. So I can see some logic to why they designed it that way.

I'm glad you raised this issue because I've only recently moved to tmux and would have been stung by it.

Could you abstract it away behind a shell alias? I used this:

   alias tmuxc='tmux new-session -t 0'